In a water treatment plant, multiple filters are used to purify water. Every so often, these filters must be "backwashed" which involves stopping the flow of water and sending backwash fluid in a reverse direction through the filters. After backwashing, there is a period of time, known as "ripening," during which water passing through the filters will require further treatment before being ready for consumers. Typically, public health authorities mandate an appropriate ripening period.
A typical filtration system for a water treatment plant is shown schematically in FIG. 1, with arrows indicating the direction in which fluid flow takes place, and with cross-fittings and T-fittings that are not specifically shown being represented by black dots as appropriate at all pipe junctions. In the plant, there are multiple filters 1, 2, 3 containing granular filter media 11, 12 13, respectively. Water enters through pipes 21, 22, 23, which have valves 31, 32, 33 in their open position, and purified water exits through pipes 41, 42, 43, respectively, with valves 51, 52, 53 open, and valves 61, 62, 63 and 71, 72, 73 shut. The purified water passes through cross-fittings 81, 82, 83 and pipes 91, 92, 93 to a common pipe 95 leading to a clearwell 96. During the filtration process, valves 101, 102, 103 on pipes 111, 112, 113 are closed.
When backwashing is required, the plant operator stops flow by closing valves 31, 32, 33 and valves 51, 52, 53. Valves 61, 62, 63 and 101, 102, 103, as well as a master valve 124, are open so that backwash occurs through common pipe 125 from backwash fluid source 126. Flow continues through pipes 131, 132, 133 and up through the filter media and out through pipes 111, 112, 113 to a waste backwash storage tank. Valve 124 is typically kept open, except for maintenance purposes. Valve 124 regulates the flow of the backwash fluid to all filters in the system. The backwash fluid source 126 usually consists of water already treated by the filter plant, and may even come from clearwell 96.
For ripening, valves 31, 32, 33 and 71, 72, 73 are open so that water flows through pipes 141, 142, 143 to common pipe 145 to a waste storage tank 146. This waste water will ultimately be retreated by the filter system.
As can readily be seen from FIG. 1, numerous valves and pipes exist in the system. Conventional wisdom teaches that all of these valves and pipes are necessary to individually backwash and to independently individually ripen filters. The backwash water requirements are kept small this way, and pipe diameters are also kept small. Moreover, the duration of time that ripening and backwashing occurs can be kept to a minimum, as these operations can be tailored to the specific requirements of each filter. Some filters may need backwashing and ripening more often than others. Although the conventional system precludes the simultaneous backwashing of filters, it does allow a filter to be backwashed while others may be ripening.